<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        #f{
            width: 800px;

        }
        #a,#b,#c,#d{
            width: 200px;
            height: 200px;
            background-color: aquamarine;
            margin: 10px;
            /*display: inline-block;*/
            float: left;

        }
        #d{

            clear: both;
        }
    </style>
</head>
<body>
    <div id="f">
        <div id="a"></div>
        <div id="b"></div>
        <div id="c"></div>
        <div id="d"></div>

    </div>

</body>
</html>